1. The Czechs weren't in the war. Chamberlain and Deladier gave the strategic western parts of Czechoslovakia to Hitler at Munich, without giving any guarantee for what was left. Hitler overran the remnants without resistance in Spring 1939. The Czech resistance was active during the war (more than the French) and they managed to assassinate Heydrich Reinhardt (getting the village of Lidice destroyed for it) but Czechoslovakia didn't exist during the war. Some Czechs did serve with the Allied armies, especially the British, but the Czech Army never saw service.
2. The Polish cavalry-attacking Nazi tanks thing is a myth invented by Nazi propaganda. It stemmed from an incident when in the confusion of retreat, some Polish cavalry got caught in the open by a Wehrmacht armored division. They fought their way out, with the sole intent of getting the hell out of there. The Nazis later spread the story that the armored division was attacked by the cavalry, as a sort of condescending comparison of Polish fighting forces to the modern Wehrmacht. Due to road conditions and harsher weather conditions in Eastern Europe, horse-mounted cavalry were far more effective much of the year than armored vehicles so right til the end of the war both the Nazis and the Soviets maintained large horse cavalry.
3. Before you knock the Polish war effort, let's compare notes a bit: Poland was attacked in September 1939 by two major military powers (Nazi Germany and the Soviet Union), was vastly outnumbered, had far fewer and less modern planes and tanks than its enemies, and was using outdated WW I-era strategies and tactics. Oh, also - Poland is essentially a flat plain, with only one river system (Vistula), with no natural barriers to hide behind. Within two weeks the unified front collapsed, and the Polish army formed army group defense zones. Warsaw finally fell on 27. September, 27 days after the Nazi attack and 10 days after the Soviet attack. The last major defense zone collapsed on 05. October, 35 days after the invasion began. 35 days.
Now let's compare this to, oh, say France, Belgium, Luxembourg and Holland. France alone had as many planes as the Germans, and a small advantage in infantry. France had a comparable number of tanks as well, though they used them very differently (i.e., less effectively). The invasion route for the Germans lead through the old WW I battlefields, which had multiple river systems and forested areas. On 10. May Hitler launched his invasion of the West; by 15. May the Dutch Army was eliminated as an effective fighting force (5 days), by the 17th the French line had been penetrated (7 days) leaving the Channel exposed and giving the BEF the impetus to head for home leaving all their equipment on the beaches of Dunkirk, on the 24th the French made their last attempt to break the German assault (but failed) and their rear areas dissolved into chaos (14 days), on the 28th the Belgians surrendered (18 days), on 10. June Paris fell, effectively ending French resistance (though some mopping-up operations still went on against the Maginot Line from behind). Total: 30 days.
Hmmm; Poland = 35 days, France + Belgium + Holland + Luxembourg + BEF = 30 days. Hmmm. Poland = Smaller army with no natural barriers, against two invaders and still lasted 35 days; France + Belgium + Holland + Luxembourg + BEF = more soldiers, more equipment, with more natural barriers, lasted 5 days less than the Poles. Hmmm.
Poles also gave the Allied cause soldiers throughout the war, making the 4th largest contribution of men after the Soviets, Americans and British. Poles fought at Narvik in Norway (The first Allied submarine victory was by a Polish submarine that sank a German transport near Bergen.), in France, in Britain (one-fifth of the pilots on the Allied side in the Battle of Britain were Poles), in North Africa, in Italy (taking Monte Cassino when American and British assaults failed) and of course in Poland itself. The Polish resistance (Armia Krajowa - AK) was the 2nd largest in Europe during the war, after the Yugoslavs. (Almost everything the Allies learned about the Holocaust during the war came from the AK.) Contrary to what a popular recent American film claims, it was Polish intelligence officers working for the British who cracked the Nazi Enigma code system. Poland lost 6 million people in the war, one-quarter (1/4) of its pre-war population. Only the Soviet Union proportionately lost as much (20 million Soviets dead = 1/4 of their pre-war population).
Although you wouldn't know it from the way it was abandoned at war's end to the Soviets, Poland's wartime contribution wasn't quite "useless".